1. Field of the Invention
The present invention relates to a molten carbonate fuel cell, and more particularly to a longer lasting and highly efficient internal reforming molten carbonate fuel cell equipped with a membrane for intercepting carbonate vapor.
2. Description of the Related Art
Generally, fuel cells are utilized to directly convert chemical energy stored in chemical compounds such as hydrocarbons into electrical energy. Among many types of fuel cells, molten carbonate fuel cells (MCFC) and solid oxide fuel cells (SOFC), usually operated at 650xc2x0 C. or above, are classified as high temperature fuel cells. These high temperature fuel cells are advantageous in that a reforming reaction can take place inside the fuel cell stack. Due to its internal reforming characteristic which allows reforming reaction to be carried out without additional external heat exchangers, much of the power plant facilities can be simplified to reduce the manufacturing cost.
However, there is a drawback in that the internal reforming catalyst used for the molten carbonate fuel cells tend to be deactivated by alkaline carbonate vapor evaporated from the electrolyte matrix, hence shortening its life time. Specifically, the internal reforming catalyst looses its catalytic activity when it comes into contact with carbonate vapor generated during the operation of the fuel cell or when it comes into contact with hydrated vapor converted from the reaction of carbonate vapor and steam, which eventually decreases the life time of the fuel cells.
Accordingly, in order to realize the use of the internal reforming molten carbonate fuel cells in practical application, there have been numerous researches related to lengthening the life of internal reforming catalyst in the carbonate fuel cell.
For example, to decrease the amount of carbonate vapor from being in contact with catalyst, U.S. Pat. No. 4,365,007 (Energy Research Corporation) discloses a method of changing the structure of the gas channel within the anode of the fuel cell and a method of inserting a porous corrugated plate inside the anode. Similarly, U.S. Pat. No. 4,467,050 suggests a method of forming an inorganic layer on a stainless steel plate by using an electrophoresis method, followed by dipping the plate in a catalytic slurry to obtain a plate coated with catalyst. Further, U.S. Pat. No. 4,788,110 discloses a method of placing a structure made from a stainless steel between the anode and pellets of catalyst and a method of inserting carbonate vapor absorption pellets between the pellets of catalyst to reduce the catalyst from being in contact with the carbonate vapor.
However, the above disclosed patents do not substantially reduce the carbonate vapors from being introduced to the catalysts. Moreover, the cell performance decreases from the increased internal resistance caused by introduction of absorption pellets made from electrical insulating material.
On the other hand, U.S. Pat. No. 4,774,152 (Mitsubishi Electric Corporation of Japan) discloses a method of coating the surface of catalyst pellets with a porous carbonate absorption material (electrolyte-sink) made substantially from Al, Si and Cr, a method of mixing with catalytic powder, and a method of forming a carbonate vapor absorption layer on top of the catalyst layer.
However, in using such carbonate absorption material to intercept carbonate vapor, the carbonate from the electrolyte matrix tends to dissipate due to the continuous transfer of carbonate to the absorption layer, resulting in the shortening of the life time of the fuel cell. Moreover, there is a further problem in that the inorganic material used for absorbing carbonate vapor increases the internal resistance of the fuel cell.
Although, the above prior art attempts to prevent the poisoning of the internal reforming catalyst from the alkaline carbonate by intercepting the flow of carbonate vapor to the catalyst or by forming a carbonate absorption layer which undesirably depletes the carbonate in the electrolyte matrix to render the fuel cell with decreased life-span, they fall short of providing a satisfactory solution. Hence, the improvement in lengthening the life time of the internal reforming catalyst in the molten carbonate fuel cell still remains to be desired.
In view of the foregoing, it is an object of the present invention to provide a highly efficient and longer lasting molten carbonate fuel cell having a membrane for intercepting carbonate vapor which significantly reduces the deactivation of the internal reforming catalyst by carbonate vapor.
In order to achieve the above object, the present invention provides an internal reforming molten carbonate fuel cell having an intercepting membrane interdisposed between an anode and catalyst. The present inventors selected nickel or nickel alloy as a base material for the intercepting membrane due to its low affinity for carbonate vapor, high electrical conductivity, and its high corrosion resistance in the anode environment over other metals or metal-oxides. Thus, in the present invention, the intercepting membrane is made of nickel or nickel alloy for intercepting carbonate vapor and/or hydrated vapor converted from the reaction between carbonate vapor and steam and placed in between anode and reforming catalyst to hinder hydrated and carbonate vapors from reaching the catalyst. The intercepting membrane also has a pore size distribution ranging from an average diameter of about 0.01 xcexcm to about 10 xcexcm, porosity of about 30% to about 80%, and a thickness of about 0.1 mm to about 1 mm.